1. Field of the Invention
The present invention relates to a fast channel-switching mechanism in an 802.11(h) wireless-local-area network (WLAN), wherein channel switching is performed independent from the beacon-interval period.
2. Discussion of the Related Art
The medium-access-control (MAC) layer and physical (PHY) layer characteristics for wireless-local-area networks are specified in the IEEE 802.11(h) standard, which is defined in International Standard ISO/IEC 8802-111, “Information Technology-Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific Requirements, Part 11: Wireless LAN Medium Access Control (MAC) and Physical (PHY) specifications,” 1999 Edition, which is hereby incorporated by reference in its entirety. The standard provides a mechanism for the announcement of a channel switch performed at the MAC layer. Specifically, the MAC layer provides a channel-switch announcement element that is used by an AP (Access Point) in a BSS network or a STA in an IBSS network to announce when it is changing to a new channel and the channel number of the new channel. The channel-switch-announcement element includes a “channel switch count” field which is set equal to the number of target-beacon-transmission times (TBTT's) which must transpire before the network is switched to a new channel.
A drawback of performing a channel switch in accordance with the IEEE 802.11 standard is that in certain cases there could be a considerable amount of latency, i.e., delay, in having to wait for at least one or multiple TBTT's to transpire before a channel switch is permitted. Furthermore, this latency may not satisfy the DFS (Dynamic Frequency Selection) requirement for WLANS operating in the 5 GHz band in some regulatory domains in Europe. Specifically, the DFS requirement mandates that a WLAN avoid interfering with other co-located systems, such as radar systems performing mission-critical functions. To avoid such interference, all communications must be halted in the bands where other primary users are detected within a specified time. Halting communications within the specified time may not be achievable in light of the described latency.
Accordingly, there is a need for a channel-switching scheme that can be incorporated into the IEEE 802.11 standard, at the MAC layer, which overcomes the described channel-switching latency and that also satisfies the DFS regulatory requirement imposed on WLANS operating in the 5 GHz band in Europe.